Percutaneous transluminal coronary angioplasty (PTCA) is used to reduce arterial build-up of cholesterol fats or atherosclerotic plaque. Typically a large guidewire of about 0.038 inches in diameter is steered through the vascular system to the site of therapy. A guiding catheter, for example, can then be advanced over the guidewire to a point just proximal of the stenosis. The large guidewire is then removed. A balloon catheter on a smaller 0.014 inch guidewire is advanced within the guiding catheter to a point just proximal of the stenosis. The guidewire is advanced into the stenosis, followed by the balloon. The balloon at the distal end of the catheter is inflated causing the site of the stenosis to widen. The dilatation of the occlusion, however, can form flaps, fissures and dissections which threaten reclosure of the dilated vessel or even perforations in the vessel wall. Implantation of a metal stent can provide support for such flaps and dissections and thereby prevent reclosure of the vessel or provide a patch repair for a perforated vessel wall until corrective surgery can be performed. Reducing the possibility of restenosis after angioplasty reduces the likelihood that a secondary angioplasty procedure or a surgical bypass operation will be necessary.
An implanted prosthesis such as a stent can preclude additional procedures and maintain vascular patency by mechanically supporting dilated vessels to prevent vessel collapse. Stents can also be used to repair aneurysms, to support artificial vessels as liners of vessels or to repair dissections. Stents are suited to the treatment of any body lumen, including the vas deferens, ducts of the gallbladder, prostate gland, trachea, bronchus and liver. The body lumens range in size from the small coronary vessels to the 28 mm aortic vessel. The invention applies to acute and chronic closure or reclosure of body lumens.
A typical stent is a cylindrically shaped wire formed device intended to act as a permanent prosthesis. A typical stent 10 ranges from 5 mm to 50 mm in length. A stent is deployed in a body lumen from a radially compressed configuration into a radially expanded configuration which allows it to contact and support a body lumen. The stent can be made to be radially self-expanding or expandable by the use of an expansion device. The self expanding stent is made from a resilient springy material while the device expandable stent is made from a material which is plastically deformable, i.e., malleable. A plastically deformable stent can be implanted during a single angioplasty procedure by using a balloon catheter bearing a stent which has been crimped onto the balloon. Stents radially expand as the balloon is inflated, forcing the stent into contact with the body lumen thereby forming a supporting relationship with the vessel walls. Deployment is effected after the stent has been introduced percutaneously, transported transluminally and positioned at a desired location by means of the balloon catheter.
The biocompatible metal stent props open blocked coronary arteries, keeping them from reclosing after balloon angioplasty. A balloon of appropriate size and pressure is first used to open the lesion. The process is repeated with a stent crimped on a second balloon. The second balloon may be a high pressure type of balloon, e.g., more than 12 atmospheres, to insure that the stent is fully deployed upon inflation. The stent is deployed when the balloon is inflated. The stent remains as a permanent scaffold after the balloon is withdrawn.
Various shapes of stents are known in the art. U.S. Pat. No. 4,649,922 to Wiktor for "Catheter Arrangement Having A Variable Diameter Tip and Spring Prosthesis" discloses a linearly expandable spring-like stent. U.S. Pat. No. 4,886,062 to Wiktor for "Intravascular Radially Expandable Stent and Method of Implant" discloses a two-dimensional zig-zag form, typically a sinusoidal form.
U.S. Pat. No. 5,104,404 to Wolff for "Articulated Stent" discloses a stent made up of a number of wires welded together and then connected together with hinges to provide articulation.
U.S. Pat. No. 5,443,498 to Fontaine for "Vascular Stent and Method of Making and Implanting a Vascular Stent" discloses a continuous wire which is formed into a substantially tubular body having a plurality of oblong, open cells which are staggered around the circumference of the tube. When the body is formed in its unexpanded state, the long sides of each oblong cell are arranged substantially parallel to the longitudinal axis of the tubular body. Adjoining cells may then be bonded together at a point between adjacent parallel sides on a cell. The peak apex of one wave is bonded to the adjacent valley apex of the other wave. When the body is expanded, the adjacent sides of each cell extend oblique to the longitudinal axis of the body. See also U.S. Pat. No. 5,370,683 FIGS. 10 and 11 to Fontaine.
U.S. Pat. No. 4,856,516 to Hillstead for "Endovascular Stent Apparatus and Method" discloses a wire first bent into a series of tight bends. The wire is then further bent into a sequence of loops that are connected by half hitch junctions and interconnections which are either aligned or spiral around a circumference of the stent.
U.S. Pat. No. 4,878,906 to Lindemann et al. for "Endoprosthesis for Repairing a Damaged Vessel" discloses a flexible, plastic, thin-walled sleeve molded with various types of circumferential and axial ribs and reinforcements to be used as an endovascular prosthesis.
U.S. Pat. No. 4,994,071 to MacGregor for "Bifurcating Stent Apparatus and Method" discloses a wire forming a backbone extending axially along the length of the lattice that extends away from the lattice and is used to construct the interconnecting loops.
U.S. Pat. No. 5,133,732 to Wiktor for "Intravascular Stent" discloses a stent body coiled from a generally continuous wire with a deformable zig-zag structure with a means for preventing the stent body from stretching along its longitudinal axis.
U.S. Pat. No. 5,304,200 to Spaulding for "Welded Radially Expandable Endoprosthesis and the Like" discloses terminal portions of the end circumferential sections welded directly to a portion of a generally adjacent circumferential section, and the welding preferably is carried out within an inert gas environment in a manner that minimizes crack formation at the weld locations.